1. Field of the Invention
The invention relates to a vehicle seat.
2. Description of the Related Art
FIG. 8 is a schematic view useful for explaining the reclining motion of a known vehicle seat 510. In FIG. 8, constituent elements of the vehicle seat 510 are illustrated in simplified forms, and the construction of the seat 510 is partially omitted. As shown in FIG. 8, the vehicle seat 510 is provided as a rear seat in the second row or third row in the vehicle compartment, and consists principally of a seat back 530 and a seat cushion 520. The seat back 530 of the vehicle seat 510 is mounted along a vehicle-body wall 580 formed as a part of a vehicle-body structure, such as a luggage compartment, and the seat cushion 520 is supported on the vehicle body to be slidable in the longitudinal direction of the vehicle. Also, the seat back 530 and the seat cushion 520 are coupled to each other such that they can pivot relative to each other. In FIG. 8, the seat back 530 and seat cushion 520 indicated by two-dot chain lines are those of the vehicle seat 510 that is in a normal position 510A, and the seat back 530 and seat cushion 520 indicated by solid lines are those of the vehicle seat 510 that is in a reclining position 510B.
As shown in FIG. 8, the vehicle-body structure, such as a luggage compartment, is formed behind the vehicle seat 510, and thus almost no space is provided behind the seat back 530. Therefore, the seat back 530 cannot be inclined rearwards while the seat cushion 520 is in a non-moving or stationary condition, as is the case with conventional vehicle seats. Thus, where the reclining motion of the seat back 530 is limited by the layout of the vehicle compartment, the vehicle seat 510 needs to be operated in the following manner. Initially, the seat cushion 520 that is in the normal position 510A is caused to slide toward the front of the vehicle. As a result, the seat back 530 coupled to the seat cushion 520 moves downward along the wall of the vehicle-body structure, such as a luggage compartment, which is located behind the seat back 530, and the angle between the seat cushion 520 and the seat back 530 is increased so that the vehicle seat 510 is placed in the reclining position 510B.
FIG. 9 is a schematic view useful for explaining the movement of the above-described vehicle seat 510 between the normal position 510A and the reclining position 510B with reference to a hip point HP about which the torso and thigh of a seated person M pivot and which corresponds to the hip joint of the seated person M. As shown in FIG. 9, a back contact point P of the seat back when the vehicle seat 510 is in the normal position 510A and a back contact point Q on the back of the seated person M which contacts the point P are shifted to P1, Q1, respectively, when the vehicle seat 510 is placed in the reclining position 510B. This is because, when the seat 510 is moved from the normal position 510A to the reclining position 510B, P moves about a pivot point of the seat back 530 and reaches P1 whereas Q moves about the hip point HP and reaches Q1. Similarly, an ischial contact point R of the seated person M when the vehicle seat 510 is in the normal position 510A is shifted to R1 when the vehicle seat 510 is placed in the reclining position 510B.
Due to the phenomena as described above, the positional relationship between the back contact point P at which the back of the seated person M contacts the seat back 530 and the ischial contact point R at which the tuber of ischium of the seated person M contacts the seat cushion 520 largely varies between the normal position 510A and the reclining position 510B. Therefore, the seated person M may feel uncomfortable because of a “back displacement X” that causes a shirt, or the like, which the seated person M is wearing to be pulled up during reclining, and/or a “hip displacement Y” that causes the trousers or skirt of the person M to rise up along his/her body during reclining.
The problems arising from the “back displacement X” and “hip displacement Y” are not limited to the discomfort of the seated person M caused by pull-up of the shirt, or the like, or rising of the trousers or skirt during reclining of the vehicle seat. Namely, if the relationship in position between the back contact point P of the seat back 530 and the ischial contact point R of the seat cushion 520 is largely different between the normal position 510A and the reclining position 510B, the seated person M will be seated on the vehicle seat having a different shape from that determined in the normal position 510A, in which a lumbar support, seat heater, ventilator, sensor(s) and other equipment are mounted at different locations, when the vehicle seat 510 is placed in the reclining position 510B. Also, if the headrest is adjusted to an appropriate position in the reclining position 510B, for example, the headrest will be lowered with respect to the seated person M when the seat 510 is placed in the normal position 510A, thus requiring an adjustment to be made again.
As described above, when the vehicle seat 510 is placed in the reclining position 510B, the seat cushion 520 is caused to slide in the forward direction of the vehicle so that the seat back 530 can be inclined. Therefore, in the arrangement where an ottoman device 522 for supporting the crura of the seated person M is mounted to a front end portion of the seat cushion 520, space in front of the toes of the person M is undesirably reduced when the vehicle seat 510 is placed in the reclining position 510B and the seated person M takes a relaxed posture with his/her feet extending forward. Furthermore, when the vehicle seat 510 is placed in the reclining position 510B, the amount of overlap of the seat back 530 with the seated person M increases to Z2 as indicated in FIG. 9, though the amount of overlap is Z1 (<Z2) when the vehicle seat 510 is in the normal position 510A. However, the seated person M does not sink into the seat back 530 by the theoretical amount of overlap Z2, when the vehicle seat 510 reclines. As a result, the seated person M is bounced forward due to the force applied from a cushion pad of the seat back 530, and is pushed further forward in the longitudinal direction of the vehicle, resulting in a further reduction of the space in front of the toes.
One example of vehicle seat that is less likely to suffer from the “back displacement” as described above is described in Japanese Patent Application Publication No. 7-327768 (JP-A-7-327768). The vehicle seat described in JP-A-7-327768 is arranged to reduce a displacement of the back contact point on the seat back of the seat in the reclining position from that of the seat in the normal position, by sliding the seat cushion forward and moving the seat cushion up and down by a link mechanism.
However, if the movement of the back contact point on the seat back between the normal position and the reclining position is observed with reference to the hip point, the seat of JP-A-7-327768 is arranged only to reduce the back displacement, but still cannot eliminate the back displacement. Also, the above-mentioned problems of “hip displacement on the seat cushion” and “reduction of the space in front of the toes of the seated person in the reclining position” are still not solved with the seat of JP-A-7-327768.